Detailed Description of Error P0391
OBDII error code P0391 is a generic trouble code that indicates a problem with the Camshaft Position (CMP) sensor B, bank 2 – circuit range/performance. This code is triggered when the Engine Control Module (ECM) detects an abnormal signal from the CMP sensor B, which is responsible for monitoring the camshaft position on bank 2 of the engine.
The CMP sensor B is usually located on the valve cover or cylinder head and provides the ECM with information about the camshaft''s rotational position and speed. This information is used to synchronize fuel injection, ignition timing, and variable valve timing (if equipped). When the ECM receives an abnormal signal from the CMP sensor B, it sets the P0391 code and illuminates the Check Engine Light (CEL).
Possible Causes of Error P0391
- Faulty Camshaft Position (CMP) sensor B
- CMP sensor B circuit wiring or connector damage
- CMP sensor B circuit short to ground or power
- Faulty Engine Control Module (ECM)
- Corrupted ECM software or programming
- Camshaft position sensor B mounting or installation issue
- Low battery voltage or weak battery
- Faulty or worn-out camshaft or valve train components
- Engine mechanical problems, such as low compression or engine oil leaks
Possible Fixes for Error P0391
- Inspect the CMP sensor B wiring and connector for damage or corrosion and repair or replace as needed
- Check the CMP sensor B circuit for shorts to ground or power and repair or replace as needed
- Replace the faulty CMP sensor B with a new one
- Update or reflash the ECM software or programming
- Inspect and clean the CMP sensor B mounting or installation area
- Check and charge the battery to ensure proper voltage
- Inspect and replace faulty or worn-out camshaft or valve train components
- Perform a thorough engine mechanical inspection to identify and address any underlying issues
